agridat (version 1.12)

wiebe.wheat.uniformity: Uniformity trial of wheat

Description

A uniformity trial of 1500 plots of wheat conducted in Idaho in 1927.

Format

A data frame with 1500 observations on the following 3 variables.

row

Row

col

Column (series)

yield

Yield in grams per plot

Details

Yield trial conducted in 1927 near Aberdeen, Idaho. The crop was Federation wheat (C.I. no 4734). Plots were seeded on April 18 with a drill that sowed eight rows at a time. Individual rows were harvested in August and threshed with a small nursery thresher.

Rows were 15 feet long, 1 foot apart.

Some authors recommend analyzing the square root of the yields.

References

D.A. Preece, 1981, Distributions of final digits in data, The Statistician, 30, 31--60.

Wilkinson et al. (1983). Nearest Neighbour (NN) Analysis of Field Experiments. J. R. Statist. Soc. B, 45, 151-211.

Examples

# NOT RUN {
data(wiebe.wheat.uniformity)
dat <- wiebe.wheat.uniformity

require("lattice")
# 125 rows = 125 feet tall. 12 cols * 15 feet = 180 feet wide.
desplot(yield~col+row, dat, aspect=125/180, flip=TRUE,
  main="wiebe.wheat.uniformity: yield") # row 1 is at south

# Preece (1981) found the last digits have an interesting distribution
# with 0 and 5 much more common than other digits.
dig <- substring(dat$yield, nchar(dat$yield))
dig <- as.numeric(dig)
hist(dig, breaks=0:10-.5, xlab="Last digit",
     main="wiebe.wheat.uniformity - histogram of last digit")
table(dat$col, dig) # Table 3 of Preece

# Loess
# m3 <- loess(yield~row+col, dat)
# plot(dat$row, resid(m3), ylim=c(-300,300),
#      main="wiebe.wheat.uniformity")

# Wilkinson (1983, p. 152) noted that an 8-row planter was used which
# produced a recurring pattern of row effects on yield.  This can be seen
# in the high autocorrelations of row means at lag 8 and lag 16
rowm <- tapply(dat$yield, dat$row, mean)
acf(rowm, main="wiebe.wheat.uniformity row means")
# Plot the row mean against the planter row unit 1-8
xyplot(rowm~rep(1:8, length=125),
       main="wiebe.wheat.uniformity",
       xlab="Planter row unit", ylab="Row mean yield")

# }